Inline Exhaust Fans: How to Use Them to Vent Multiple Bathrooms

Updated: May 17, 2024

Add one attic fan to vent multiple bathrooms.

If you have two bathrooms that are close together and one has an exhaust fan and the other doesn’t, you might be wondering if you can tie a new exhaust duct into the existing one. Well, you can’t! You’d often blow air from one bathroom into the other, and local building inspectors wouldn’t approve it.

But while you can’t have two fans with one vent, you can make one fan and one vent serve two bathrooms. This setup requires an in-line exhaust fan.

Read on to learn about installation costs, how to buy the right size and how to know if an inline exhaust fan is the right solution for your venting needs. Three industry pros, Matthew Labrecque from All Air HVAC, Jay Ryan from Boulanger’s Plumbing and Heating and Peter Glover from Glover’s Plumbing offer pro tips and insights on this versatile exhaust fan option.

What Is an Inline Exhaust Fan?

An inline — or remote — exhaust fan is a type of home ventilation fan installed within the ductwork. These fan types are typically mounted in the attic, rather than in the room it ventilates.

A common use for inline exhaust fans is to vent two bathrooms. A plastic exhaust grille in each bathroom (usually in the ceiling) attaches to ducts, which then fasten to a “Y” connector at the fan. From the fan, a single exhaust duct exits through the roof. Each bathroom has its own switch and operates independently.

Inline exhaust fans can also be used to move warm air throughout a home, like from a wood stove to a garage or basement, remove radon gas or vent a range hood in the kitchen.

Inline Exhaust Fans vs. Standard Bathroom Exhaust Fans

While both fans remove humidity and odors from your bathroom, each system has pros and cons.

Inline exhaust pros and cons


  • An inline vent system is quiet. Because the fan is in the attic, you’ll hardly hear it. They are also available in larger, more powerful options than any standard bath fan.
  • The inline fans perform better over longer duct lines because of the extra power.
  • They maintain their advertised cubic feet per minute (CFM) air extraction rating over longer distances.
  • Less ductwork and holes in the roof for hood vents with an inline system.


  • Applications can be limited, as you’ll need accessible attic space to install an inline fan.
  • Material and installation costs are also much higher than a standard exhaust fan.
  • Ryan points to a lack of customization options and added features as a drawback of inline fans. “An inline fan is just a fan,” he says. “It doesn’t have all the added features of a bathroom fan.”

Standard bathroom exhaust fan pros and cons


  • A standard bathroom exhaust fan is less expensive than an inline system.
  • They are easier to install yourself or cost less if hiring a pro.
  • They come with a lot of optional features, too. “You can get one with a room light, a night light, a motion sensor or humidity sensor,” Ryan says.


  • A standard bathroom exhaust fan is louder when operating than an inline fan.
  • They tend to have weaker motors and poorer suction than inline fans.
  • Each unit requires independent ductwork and an outside vent hood, which can be problematic in a home with lots of bathrooms.

How to Use an Inline Exhaust Fan to Vent More Than One Bathroom

illustration of exhaust fanFamily handyman

First, install plastic exhaust grills in each bathroom ceiling. Run 4-in. flexible ductwork from the grills to the inline fan. Connect each duct to a “Y” connector, then secure it to the inline fan. A single 6-in. duct runs from the fan to the vent hood through the roof.

Some inline fans have plugs and others are hard-wired. Each bathroom is also wired to operate independent power switches.

How to Calculate the Size of the Inline Exhaust Fan You Need

For a standard two-bathroom application, first measure each bathroom’s square footage (length X width) and add these numbers for the total square footage.

When shopping for an inline fan, look for a model with a CFM air extraction rate that is slightly more than the bathrooms’ square footage. For example, if the total is 130 sq. ft., look for a fan with a 140 to 160 CFM rating.

“You’re trying to come up with a CFM that will keep the humidity down,” Ryan says. He adds that some models come with a range of CFM that can be adjusted to suit your bathroom ventilation needs.


Can you vent a bathroom and a range hood together?

No. “A kitchen vent is considered combustible, so it needs to be on its own exhaust system,” Glover says.

How much does it cost to install an inline exhaust fan?

Expect to pay at least $2,500 to $3,000 for an inline exhaust fan installation.

Can inline exhaust fans be too big?

Yes. Oversized fans can incur higher operational costs, expel warm air from your living space, and potentially induce a vacuum effect by expelling an excessive amount of air that needs replacing.

About the Experts

  • Matthew Labrecque is the owner of All Air HVAC located in South Hadley, Massachusetts. The company specializes in heating and cooling installation and repairs, ductwork and air purification systems in new and existing homes. He has over 18 years of industry experience.
  • Peter Glover is the owner of Glover’s Plumbing in Kenner, Louisiana, a residential plumbing company. He is a Master Plumber with over fifteen years of experience.
  • Jay Ryan is HVAC project manager for Boulanger’s Plumbing and Heating in Easthampton, Massachusetts. He’s been with Boulanger’s since 2001 and holds a Master Plumber License in the State of Massachusetts.